For example: nitrogen, oxygen and hydrogen implanted metallic materials e. Ti—6Al—4V and stainless steel and polymers e. UHMWPE and PEEK used for orthopedic implants showed better wear performance than those untreated [ 91—94 ]; corrosion resistance of alloys containing hazardous elements for the health e. Studies on cell biology demonstrated that the topography of the extracellular matrix ECM could regulate stem cell behaviors and fate, such as cell growth and differentiation, via physical interactions with the cells. Such physical interactions are affected by some geometric cues in different scales, including molecular conformation, surface topography or roughness, fiber diameter and so on [ ].
The bone tissue was proposed to be divided into as many as nine levels from molecules e. For example, array patterns of mineralized collagen fibrils in nano-scale, and material patterns of woven bone, parallel fibered bone and lamellar bone in micro-scale [ ]. Therefore, behaviors and fate of osteocytes would be regulated by topographies of bone tissue in various scales. Based on the regulation effects of topography on cell behavior and fate in natural tissues, material could be functionalized by modifying surface topography, for example, creating patterns.
As early as , Harrison [ ] found the influence of topography on cell behaviors based on the observation of the relationship between the movements of embryonic cells and the material shapes in contact with the cells. As the development of nano- and micro-processing techniques, some of them have been employed to fabricate nano- and micro-patterns on biomaterial surfaces, and interactions between patterned biomaterial surfaces and cells were investigated. Surface patterning techniques are widely used and are developing rapidly in the field of microelectronics.
Recently advanced methods for surface patterning on biomaterials were partially derived from those in microelectronics industry [ ]. In this section, methodologies for the fabrication of nano- and micro-patterns on material surfaces are summarized. Photolithography was the first surface patterning technique introduced to make patterns for controlling cell behaviors [ ]. Another well-known application of photolithography in the field of biology is the fabrication of DNA arrays [ , ]. A photolithography process commonly comprises following steps as shown in Fig.
Due to the optical diffraction of the focused light beam, the resolution of the pattern created by photolithography is restricted to about half of the wavelength of the light source, typically several hundred nanometers [ ].
Therefore, photolithography is suitable to create patterns with the size comparable to a cell. Above classic photolithography with mask is an indirect approach for the fabrication of surface patterns. As the advance of photolithography, a direct-write mode without using mask has been developed via using a focused light beam to fabricate pattern directly on material surface [ — ].
Surface Engineering of Multifunctional Nanocomposites for Biomedical Applications: a Brief Update
In this maskless photolithography, laser is more commonly used as the light source to provide high-intensity light beam for the fabrication of surface patterns. In order to fabricate patterns, the light beam may induce two types of reactions on material surface: one is photochemical reaction for photoactive surfaces [ ], the other is physical reactions involving ablation, melt or deformation of the substrate caused by the high energy of the laser [ , ].
Some typical examples by using direct-write photolithography are: Pfleging et al. With the similar principle and fabrication process to photolithography, electron beam lithography EBL is able to create nano-sized patterns on material surfaces, since the electron beam is considered as a de Broglie wave, the wavelength of the electron is much shorter than that of light beams [ ]. For example, a typical electron beam provided by electron microscope is accelerated by kV electric field, and the wavelength is 0. EBL is used to make patterns on electron sensitive material surfaces, which would be crosslinked [ , ], chemically transformed [ , ], polymerized [ ] and so on under the electron beam.
For example, Idota et al. In spite of the high spatial resolution in nano-scale, EBL has its own limitations, such as high cost and low throughput. Therefore, EBL is now more commonly investigated in laboratory, rather than industrialization applications. Moreover, EBL was used to fabricate special patterns that gave extraordinary functions to material surfaces.
Wang et al. Such interesting effects were further investigated and many similar multi-functional patterned surfaces were developed [ , ]. DPN uses a tip of atomic force microscope to create patterns by directly writing on the surface using a variety of molecular inks solutions of molecules. In biomedical applications, DPN has been used to create patterns with polymers [ — ], biomolecules including proteins [ ], peptides [ ], lipids [ , ], enzymes [ ] and DNA [ ] , nano-particles [ — ], as well as living cells [ , ], onto different substrates.
Similar to other nano-patterning techniques mentioned above, the throughput of DPN is relatively low. To overcome such disadvantage, a high-throughput DPN was developed by parallelly operating a 2D probe arrays consisted of 55 tips [ ]. Nano-imprinting and engraving uses a hard stylus to indent or scratch material surface to create patterns.
Thus, the process is destructive to the surface. By using this process, nano-patterns were created on thin film such as self-assembly monolayer coated surface [ ]. Moreover, nano-patterns of proteins were fabricated by grafting protein molecules onto the exposed substrate after the scratching [ , ]. Typically, as shown in Fig.
In this patterning technique, the mold contacts with the substrate to transfer the patterns onto the surface by the molecular inks. As early as s, Singhvi et al. Another example is the regulation of cell fate by patterning with master: Kilian et al.
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Patterning with master has also been used to patterning proteins [ , ], DNA [ ] and cells [ , ] for biomedical applications. Another process is imprinting with master, which uses a template made of hard material for creating patterns on the substrate [ ]. Imprinting with master makes mechanically deformation on material surface to form patterns. Therefore, the master for imprinting must be hard enough to fabricate patterns on a relatively soft substrate.
By combining imprinting with master and lithography, nanoimprint lithography NIL creates nano-patterns on a substrate by imprinting a mold with the nano-patterns into a resist coated on the substrate and subsequent etching process. NIL was firstly reported in by Prof.
The Leibniz Institute of Surface Engineering (IOM)
Chou and his coworkers [ ]. They prepared a mold of nano-patterned silicon dioxide by EBL and etching, and then transferred the pattern to a PMMA resist coated on a silicon substrate by indenting to form patterned resist with different thickness, followed by anisotropic etching to finally transfer the pattern onto the substrate.
Such NIL process used a nano-template to create pattern, rather than by using a stylus, brought about relatively higher throughput.
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NIL has been used to create nano-patterns on various substrates for biomedical applications [ — ], or fabricate polymers [ , ], proteins [ — ] and DNA [ ] patterns on the substrates. Self-assemble is an energy-saving process to prepare patterns. During the self-assemble, intermolecular or inter-particle forces make molecules or nano-particles arranged in a regular pattern, in order to minimize total free energy of the entire surface.
Molecules or nano-particles can self-assemble in an area ranging from nano-scale to micro-scale. Many types of materials were employed in self-assemble fabrication of patterns, such as block copolymers [ — ], nano-spheres [ , ], nano-particles [ ], biomolecules [ , ] and so on. Since the cells live and act in a 3D physiological environment in natural tissues and organs, 3D patterns on biomaterial surfaces would provide spatial architectures closed to physiological conditions and beneficial for tissue reconstruction and repair.
As a result, 3D patterning technique is becoming an attractive research hotspot in the field of surface modification. In the present review paper, 3D patterning does not refer to a specific patterning techniques, many of those described in previous sections could be used to create 3D patterns via minor modifications or by combining with other techniques.
Two-photon lithography TPL and multiphoton lithography MPL are direct-write technique that is capable of creating 3D patterns on polymeric surfaces by laser beam. During a TPL or MPL process, two-photon or multiphoton absorption occurs at a photosensitive surface by attaining energy from the laser beam, thereby chemical reactions usually polymerization take place to form 3D patterns at the laser spot.
For example, Nielson et al. Besides replicated patterns, crosslinked protein with unstrained structures in micro-scale could be fabricated using MPL [ ]. For biomedical applications, MPL can be used to fabricate micro-patterns or 3D structures with proteins [ — ], hydrogels [ — ], bioabsorbable polymers [ , ], gelatin [ , ] and so on.
Interference lithography IL , which is also called holographic lithography or interference holography, uses interference patterns formed by two coherent laser beams to build periodic 3D patterns. By adjusting parameters e.
During an IL process, the interfering laser beams can be used to induce polymerization reactions to create 3D patterns on a substrate. The advantage of IL is that the patterning process is simple without using masks, and the throughput is relatively higher than other patterning processes. However, the alignment of the coherent beams is complex, and any changes for the patterns need to simultaneously adjust both beams.
Although IL was developed in recent decade and relatively widely used in the field of microelectronics or optoelectronics [ — ], this technique has also been employed to fabricate patterns on materials for biomedical applications. For example, Prodanov et al. Various surface modification techniques commonly used for bone-related implants are reviewed in this article.
valceecimilry.gq In practical terms, one approach would be chosen from various feasible candidates for surface modification according to the target effect and physiochemical properties of the substrate, also cost as an important factor. As comprehensive utilization of multiple methods is often required to fulfill the needs, it is necessary to fully understand the principles and effects of such many modification techniques, and their latest advances prior to the processing.
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